Chelates for the regulation of metal-deficiency phenomena in plants

ABSTRACT

N-carboxymethyl-N-(hydroxybenzyl)-asparagic acids which may be further substituted in the phenyl nucleus possess metal-chelating properties for metals such as iron magnesium, calcium, manganese, cobalt, nickel, copper, zinc, cadmium or related metals. Chelates of this type may be used for the regulation of metal-deficiency phenomena in plants.

This is a divisional of application Ser. No. 292,708, filed on Sept. 27,1972 now U.S. Pat. No. 3,855,286.

The present invention relates to new chelating agents and their metalcomplexes, also to agents and processes for the regulation ofmetal-deficiency phenomena in plants by application of the new chelatesor of agents containing them.

The new chelating agents are to be understood as being asparagic acidderivatives, and correspond to the formula: ##STR1## wherein R₁represents hydrogen, hydroxy, halogen, sulpho, carboxyl, alkyl, alkoxy,alkylthio, halogenoalkyl, dialkylamino, acyl or phenyl,

R₂ represents hydrogen, hydroxy, halogen, alkyl or alkoxy, and

R₃ represents hydrogen or alkyl.

Alkyl radical R₁, R₂ and R₃ in formula I are radicals having 1 to 6carbon atoms in a straight or branched chain, such as the methyl, ethyl,n-propyl or isopropyl radical, as well as the n-butyl, n-pentyl andn-hexyl radicals and their isomers. These radicals form also the alkylmoiety of alkoxy, alkylthio, halogenoalkyl and dialkylamino radicals. Tobe mentioned as acyl radicals are, in particular, alkanoyl radicals,such as the acetyl or propionyl radical. Halogen denotes preferablychlorine or bromine.

The chelating agents according to the invention are obtained by thereaction of maleic acid and glycine to give N-carboxymethyl-asparagicacid of formula II ##STR2## and the subjecting of this, in a mannerknown per se, to the Mannich reaction with formaldehyde and a phenol offormula III ##STR3## wherein R₁, R₂ and R₃ have the meanings definedunder formula I.

The reactions are preferably performed in aqueous solution. For theproduction of N-carboxymethyl-asparagic acid, it is advisable to add analkali metal hydroxide such as sodium or potassium hydroxide. As isknown, aqueous solutions are employed for the Mannich reaction,including weakly alkaline aqueous solutions and mixtures of water withorganic solvents such as alkanols, dioxane, benzene, toluene or glacialacetic acid. It is also possible to use one of the reactants in excessas solvent, provided that the procedure does not affect the course ofthe reaction. The formaldehyde is preferably used in aqueous solution,or in the form of paraldehyde.

With the use of glacial acetic acid as solvent for the Mannich reaction,an alkali metal acetate is preferably added. The chelating agentsaccording to the invention are obtained principally as monoalkali metalsalts, and can be employed direct for the production of the metalcomplexes. Cationic exchange and subsequent crystallisation are appliedto obtain, if desired, the free o-hydroxy-benzyl-asparagic acids.

The monoalkali metal salts of the new chelating agents can be optionallyconverted, by ion exchange, into ammonium salts; the corresponding di-or trialkali metal salts and di- or triammonium salts are obtained byreaction with alkali metal hydroxides and with ammonia, respectively.

The compounds according to the invention form metal complexes with iron,magnesium, calcium, manganese, cobalt, nickel, copper, zinc, cadmium, orrelated metals. For this purpose, the chelating agents are reacted, inthe presence of water, or a mixture of water with alkanols such asmethanol or ethanol, or with tetrahydrofuran, either with a metalhydroxide, preferably in an inert gas, or with a metal salt with theaddition of alkali metal hydroxides. The reaction temperatures arebetween 0° and 100° C.

The new chelating agents of formula I can moreover be obtained by:

(a) use of bromosuccinic acid instead of maleic acid, and carrying outof the further reactions in the described manner;

(b) condensation of asparagic acid with formaldehyde and a phenolaccording to the Mannich reaction, and reaction of the intermediate withchloroacetic acid;

(c) reaction of the intermediate of formula II with ano-hydroxy-benzyl-halide;

(d) reaction of o-hydroxybenzylamine either with maleic acid and thenwith chloroacetic acid, or with chloroacetic acid firstly and then withbromosuccinic acid.

In the case of reactions with chloroacetic acid, phenolic hydroxylgroups should be protected; for example, by conversion into thecorresponding carbonic acid esters. For the reaction too according toc), the o-hydroxylbenzyl halide can be used in the form of a carbonicacid ester.

The process according to the invention for the production of the newcompounds of formula I is illustrated by the following examples. Thetemperatures are given in degrees Centigrade. New compounds of formula Iwhich can be produced by the described processes are listed in theattached table.

Production of asparagic acid derivatives

(a) An amount of 196 g of maleic acid anhydride is stirred in 200 ml ofwater at room temperature for one hour. Additions are then made, at atemperature of 75° - 80°, of 172 g of 50% sodium hydroxide solution, andsubsequently of 150 g of glycine in 120 ml of water and 160 g of 50%sodium hydroxide solution. The solution is refluxed for 48 hours, andafterwards allowed to cool to room temperature. The pH-value is adjustedto 1 by the addition of hydrochloric acid, and the formed precipitatefiltered off. The filtrate is concentrated by evaporation to obtain asemifluid consistency; the crude product is then filtered off, washedwith acetone and dried. The obtained N-carboxymethyl-asparagic acidstill contains 50 - 55% of sodium chloride, and is used without furtherpurification for the following stage of synthesis.

The pure hydrochloride of N-carboxymethyl-asparagic acid, which melts at170° C. with decomposition, can be obtained by reaction with glacialacetic acid and concentrated hydrochloric acid.

(b) An amount of 122 g of 47% N-carboxymethyl-asparagic acid issuspended in 150 ml of glacial acetic acid and 40.8 g of sodium acetate,and an addition then made of 26.5 g of 36% formalin solution and 48.7 gof 4-methyl-phenol. The reaction mixture is stirred for 20 hours at 60°,and then cooled to room temperature. The sodium chloride is separated byfiltration, and washed with 100 ml of glacial acetic acid. An additionis made to the filtrate of 1450 ml of acetone. The colourlessprecipitate is isolated, washed with 100 ml of glacial aceticacid/acetone 1:5, then repeatedly with acetone, and dried at 70°/12 Torrfor 24 hours. The obtained monosodium salt ofN-(2-hydroxy-5-methyl-benzyl)-N-carboxymethyl-asparagic acid stillcontains 0.3 equivalent of sodium acetate and one equivalent of water;it melts from 150° with decomposition.

(c) An amount of 9.5 g (0.05 mole) of N-carboxymethyl-asparagic acid isdissolved in a mixture of 40 ml of water and 37.5 ml of 2N NaOH (0.075mole), and the solution heated to 60° C. Additions are then successivelymade of 8.2 g of a 36.6% aqueous solution of formaldehyde (0.0625 mole)and 7.65 g (0.0625 mole) of 2,4-dimethylphenol, and stirring maintainedfor 40 hours at 60° C. The reaction mixture is cooled, and extracted 2 -3 times with a mixture of ether/toluene (1:1). The content ofN-(2-hydroxy-3,5-di-methyl-benzyl)-N-carboxymethyl-asparagic acid in theaqueous solution is colorimetrically determined as iron complex andamounts to 66%.

Production of iron(III)-complexes

(a) An amount of 16.2 g of anhydrous iron(III)chloride and one of 150 mlof 2N sodium hydroxide solution are heated to 90°. Theiron(III)hydroxide suspension, cooled to room temperature, iscentrifuged, the solid part separated, and repeatedly washed with waterThe iron(III)hydroxide isolated in this manner is suspended in 400 ml ofwater; 36 g of monosodium salt ofN-(2-hydroxy-5-methyl-benzyl)-N-carboxymethyl-asparagic acid is added tothe suspension, and the whole stirred for 4 hours at 90°-95° in anitrogen atmosphere. A violet solution is formed. After the solvent hasbeen distilled off, there remains the monosodium salt ofN-(2-hydroxy-5-methyl-benzyl)-N-carboxymethyl-asparagicacid-iron(III)-complex, which melts from 260° with decomposition.

(b) An amount of 36 g of monosodium salt ofN-(2-hydroxy-5-methyl-benzyl)-N-carboxymethyl-asparagic acid issuspended in 200 ml of ethanol, and an addition then made, withstirring, of 16.2 g of iron(III)chloride (anhydrous) in 100 ml ofethanol. there is subsequently made an addition of 12 g of sodiumhydroxide in 70 ml of ethanol, and the reaction mixture stirred for afurther two hours. The solvent is distilled off to obtain the monosodiumsalt of N-(2-hydroxy-5-methyl-benzyl)-N-carboxymethyl-asparagicacid-iron(III)-complex. The product still contains 5 - 6% of water and24 - 25% of sodium chloride, and yields the following analysis values:

Calculated: C 28.7; N 2.1; Fe 8.4%; Found: C 28.5; N 2.0; Fe 8.1%

(c) An amount of 3.2 g (0.01 mole) ofN-(2-hydroxy-3,5-dimethyl-benzyl)-N-carboxymethyl-asparagic acid issuspended in 50 ml of H₂ O, and an addition made of 0.4 g of NaOH (0.01mole) and 0.61 g of Fe-powder (0.011 mole).

The mixture is heated to 40° and, at this temperature, a vigorous flowof air passed through the mixture for 15 - 20 hours. The pH-value ismaintained at 3.5 during the entire reaction (addition of hydrochloricacid, if necessary). The end of the reaction is determined byspectrometrical control measurement.

The solution is filtered, and concentrated by evaporation to dryness.The monosodium salt ofN-(2-hydroxy-3,5-dimethyl-benzyl)-N-carboxymethyl-asparagicacid-iron(III)-complex is thus obtained.

Production of the calcium complex

An amount of 21.7 g of the monosodium salt ofN-(2-hydroxy-3,5-dimethyl-benzyl)-N-carboxymethyl-asparagic acid (80%)is dissolved in 100 ml of water; 5.55 g of calcium chloride in 30 ml ofwater is then added at room temperature, and subsequently 6 g of sodiumsalt in 30 ml of water; the reaction mixture is then concentrated byevaporation to dryness to obtain the disodium salt ofN-(2-hydroxy-3,5-dimethyl-benzyl)-N-carboxymethyl-asparagic acid-calciumcomplex; the decomposition point is ca. 260°.

Ca-content: calculated: 6.0%, found: 6.2%

The metal complexes ofN-(2-hydroxy-3,5-dimethylbenzyl)-N-carboxymethyl-asparagic acid given inthe following table are obtained by the process described above.

    ______________________________________                                        Metal ion   λmax (nm)                                                                             pH                                                 ______________________________________                                        Mn ++       283.340 (S)    7                                                  Zn ++       285            7.02                                               Cu ++       430.745        7.02                                               Fe +++      503            7.0                                                Co ++       480.500 (S)    7.01                                               ______________________________________                                         (S) = shoulder                                                           

The following alkali metal salts and ammonium salts of compounds offormula I are obtained by the process previously described:

    ______________________________________                                        (I)                                                                            ##STR4##                                                                     Compound                         Type  Decomposi-                             No.      R.sub.1   R.sub.2 R.sub.3                                                                             of salt                                                                             tion point                             ______________________________________                                        1        H         H       H     Na     93°                            2        5-CH.sub.3                                                                              H       H     Na    150°                            3        5-Cl      H       H     Na    160°                            4        5-OCH.sub.3                                                                             H       H     Na    150°                            5        3-CH.sub.3                                                                              5-CH.sub.3                                                                            H     Na    160°                            6        5-OH      H       H     Na    170°                            7        5-t-C.sub.5 H.sub.11                                                                    H       H     Na    170°                            8        5-C.sub.2 H.sub.5                                                                       H       H     Na    115°                            9        5-C.sub.6 H.sub.5                                                                       H       H     Na    175°                            10       5-t-C.sub.4 H.sub.9                                                                     H       H     Na    160°                            11       4-CH.sub.3                                                                              H       H     Na    150°                            12       5-t-C.sub.4 H.sub.9                                                                     3-CH.sub.3                                                                            H     Na    160°                            13       5-SCH.sub.3                                                                             H       H     Na                                           14       5-Br      H       H     Na    170°                            15       3-CH.sub.3                                                                              H       H     Na                                           16       3-COOH    H       H     Na                                           17       5-SO.sub.3 Na                                                                           H       H     Na    77-85°                          18       5-COCH.sub.3                                                                            H       H     Na    125°                            19       4-N(CH.sub.3).sub.2                                                                     H       H     Na                                           20       4-CF.sub.3                                                                              H       H     Na    120°                            21       4-OH      6-OH    H     Na                                           22       3-OH      4-OH    H     Na     95°                            23       4-OCH.sub.3                                                                             6-OCH.sub.3                                                                           H     Na                                           24       3-OCH.sub.3                                                                             4-OCH.sub.3                                                                           H     Na    147°                            25       3-Cl      5-Cl    H     Na    130°                            26       3-CH.sub.3                                                                              4-CH.sub.3                                                                            6-CH.sub.3                                                                          Na                                           ______________________________________                                    

Chelating agents are already known and have been employed in manycommercial fields of application. The chelating agent with the widestsphere of application is ethylenediaminetetraacetic acid. It is alreadyknown that metal complexes of ethylenediaminetetraacetic acid, as wellas of other chelating agents, are used for the correction ofmetal-deficiency phenomena, which occur, for example, in plants. Thus,the iron chelate of ethylenediaminetetraacetic acid is used for thetreatment of asiderosis, which occurs in the case of citrus plantsgrowing in acid soil. It is known, however, that this chelate isunstable in neutral or slightly alkaline solution, the resultingdecomposition producing the iron(III)hydroxide and a soluble salt ofethylenediaminetetraacetic acid. Consequently, this chelate cannot beemployed with any great measure of success for the correction ofmetal-deficiency phenomena occurring in plants growing in alkaline soil.

There has been the suggestion made recently that the iron chelates ofhydroxyethylenediamine triacetic acid, and of certainethylene-bis-(α-imino-o-hydroxyphenylacetic acids), likewise be used forplant nutrition. These chelates are somewhat more effective than thechelates of ethylenediaminetetraacetic acid; however, they do notpossess the desired stability over a wide pH-range. (Brit. Pat. No.832,989).

The new asparagic acid derivatives of formula I are excellentcomplex-forming agents. The chelates formed with the most diverse metalsare stable over a wide pH-range. They are thus suitable for thecorrection of metal-deficiency phenomena occurring in plants growingboth in acid and in alkaline soils.

A particular advantage of the new chelates is their effectiveness afterapplication to parts of plants above the soil. Chelates known hithertohave an unsatisfactory action when applied in this manner; they have tobe worked into the growth substrate. The new chelates are thereforeespecially valuable for application in the cultivation of vines, ofstone and pomaceous fruit, or of cultivated plants.

By virtue of the excellent properties of their chelates, asparagic acidderivatives of formula I a are preferred: ##STR5## The symbols in thisformula have the following meanings: R₄ represents hydrogen, hydroxy,halogen, sulpho, carboxyl, alkyl, alkoxy, alkylthio or phenyl, and

R₅ represents hydrogen, halogen, alkyl or alkoxy.

Alkyl radicals R₄ and R₅ contain 1 to 6 carbon atoms in a straight orbranched chain; they are, for example, those given on page 2. Thosehaving 1 to 4 carbon atoms form the alkyl moiety of alkoxy or alkylthioradicals. Halogen represents chlorine or bromine.

The following tests show the action of iron complexes of asparagic acidderivatives against chlorosis:

1. Tomato plants with clear chlorosis symtoms are placed into a nutrientsolution containing the iron chelate in concentrations of respectively 1and 0.3 mg of iron per liter. The pH-value is stabilised at 7.5 - 8 by abuffer solution. The test is evaluated after 14 days.

Evaluation:

1 = 0% effectiveness = leaves completely yellow,

4 = 100% effectiveness = leaves dark green,

2+3 = ca. 30 - 65% effectiveness, i.e. leaves yellowish green to lightgreen.

    ______________________________________                                        Iron complex of                                                                            Concentration Fe.sup.+++ /liter                                  ______________________________________                                        compound No. 1 mg          0.3 mg                                             ______________________________________                                        1            4             4                                                  3            4             4                                                  4            4             4                                                  5            4             3                                                  6            4             3                                                  7            4             4                                                  8            4             4                                                  12           4             4                                                  14           4             3                                                  24           4             4                                                  ______________________________________                                    

2. Soya beam plants are germinated in quartz sand, and then planted inspecial alkaline soil (pH 7.8 in water). When the uppermost leavesdisplay severe chlorosis symtoms the iron chelates are mixed in solidform with the topmost layer of soil, and distributed by watering. Theconcentrations are 1, 0.3 and 0.1 mg of iron per pot of three plants. Anassessment is made after 14 days of the colouration of the leaves,applying the scale of values defined in the 1st test. The commercialproduct, Na/Fe-diethylenetriaminepentaacetic acid (= Sequestren 330 Fe®) taken as a comparison produced, compared with the iron chelates ofthe present invention, only a slight change of colour of the leaves fromyellow to green.

    ______________________________________                                        Iron complex of                                                                              Concentration Fe.sup.+++ /pot                                  ______________________________________                                        Compound No.   1 mg      0,3 mg    0.1 mg                                     ______________________________________                                        1              3,8       3,5       1,5                                        2              3,8       2,5       1,3                                        3              3,3       2         1                                          4              3,5       1,5       1,3                                        5              4         3,3       2,3                                        7              4         3,5       1,7                                        8              4         3,3       1,5                                        11             3,2       2,7       1,3                                        12             3,8       3,5       2,5                                        14             4         3,2       2                                          24             4         3,2       1,8                                        Sequestren 330 Fe                                                                            2         1         1                                          ______________________________________                                    

3. Cucumber plants are germinated in quartz sand, and then placed intoan iron-free nutrient solution until the leaves are yellow (chlorotic).The iron chelate in a concentration of 300 mg of iron per liter issubsequently sprayed on to the plants, these being afterwards leftstanding in the Fe⁺⁺⁺ -free nutrient solution. An assessment of leafcolouration is made 14 days after application, the basis for evaluationbeing the scale of values used in the first test.

    ______________________________________                                        Iron complex of  Concentration Fe/liter                                       Compound No.     300 mg                                                       ______________________________________                                         1               2.5                                                          6                2.7                                                          14               2.8                                                          Sequestren 330 Fe                                                                              2                                                            ______________________________________                                    

There are moreover other uses for the new asparagic acid derivatives offormula I; for example, in the metal-working industry, where they can beused for the prevention of rust and of other oxide films. They can alsobe used in the detergent and bleach industry; e.g., for the removal ofundesirable metal traces.

Agents according to the invention are produced in a manner known per seby the intimate mixing and grinding of metal complexes of compounds ofthe general formula I, referred to in the following as "activesubstances", with suitable carriers, optionally with the addition ofdispersing agents or solvents which are inert to the active substances.The active substances can be obtained and applied in the followingforms:

solid preparations: dusts, scattering agents, granulates, (coatedgranulates, impregnated granulates and homogeneous granulates);

water-dispersible concentrates of the active substance: wettablepowders;

liquid preparations: solutions.

The solid preparations (dusts, scattering agents, granulates) areproduced by the mixing of the active substances with solid carriers.Suitable carriers are, e.g. kaolin, talcum, bole, loess, chalk,limestone, ground limestone, Attaclay, dolomite, diatomaceous earth,precipitated silicic acid, alkaline-earth silicates, sodium andpotassium aluminium silicates (feldspars and mica), calcium andmagnesium sulphates, magnesium oxide, ground synthetic materials,fertilisers such as ammonium sulphate, ammonium phosphate, ammoniumnitrate, urea, ground vegetable products such as bran, bark dust,sawdust, ground nutshells, cellulose powder, residues of plantextractions, active charcoal, etc., alone or in admixture with eachother.

The particle size of the carriers is for dusts advantageously up toabout 0.1 mm; for scattering agents from about 0.075 mm to 0.2 mm; andfor granulates 0.2 mm or coarser.

The concentrations of active substance in the solid preparation formsare from 0.5 to 80%.

To these mixtures may also be added additives stabilising the activesubstance, and/or non-ionic, anion-active, and cation-active substances,which, for example, improve the adhesiveness of the active substances onplants and on parts of plants (adhesives and agglutinants), and/orensure a better wettability (wetting agents) and dispersibility(dispersing agents). Suitable adhesives are, for example, the following:olein/lime mixture, cellulose derivatives (methyl cellulose,carboxymethyl cellulose), hydroxyethylene glycol ethers of monoalkyl anddialkyl phenols having 5 to 15 ethylene oxide radicals per molecule and8 to 9 carbon atoms in the alkyl radical, ligninsulphonic acid, itsalkali metal and alkaline-earth metal salts, polyethylene glycol ethers(carbowaxes), fatty alcohol polyethylene glycol ethers having 5 to 20ethylene oxide radicals per molecule and 8 to 18 carbon atoms in thefatty alcohol moiety, condensation products of ethylene oxide, propyleneoxide, polyvinyl pyrrolidones, polyvinyl alcohols, condensation productsof urea and formaldehyde, as well as latex products.

Water-dispersible concentrates of active substance, i.e. wettablepowders, are agents which can be diluted with water to obtain anydesired concentration. They consist of active substance, carrier,optionally additives which stabilise the active substance,surface-active substances, and anti-foam agents and, optionally,solvents. The concentration of active substance in these agents is 5 to80%.

The wettable powders are obtained by the mixing and grinding of theactive substances with dispersing agents and pulverulent carriers, insuitable devices, until homogeneity is attained. Suitable carriers are,e.g. those previously mentioned in the case of solid preparations. It isadvantageous in some cases to use mixtures of different carriers. Asdispersing agents it is possible to use, e.g. condensation products ofsulphonated naphthalene and sulphonated naphthalene derivatives withformaldehyde, condensation products of naphthalene or ofnaphthalenesulphonic acids with phenol and formaldehyde, as well asalkali, ammonium and alkaline-earth metal salts of ligninsulphonic acid,also alkylaryl sulphonates, alkali metal salts and alkaline-earth metalsalts of dibutyl naphthalenesulphonic acid, fatty alcohol sulphates suchas salts of sulphated hexadecanols, heptadecanols, octadecanols, andsalts of sulphated fatty alcohol glycol ether, the sodium salt of oleylmethyl tauride, ditertiary acetylene glycols, dialkyl dilauryl ammoniumchloride, and fatty acid alkali-metal and alkaline-earth metal salts.

Suitable anti-foam agents are, for example, silicones.

The active substances are so mixed, ground, sieved and strained with theabove mentioned additives that the solid constitutent in the case ofwettable powders has a particle size not exceeding 0.02 to 0.04 mm.

Furthermore, the agents according to the invention can be used in theform of solutions. For this purpose the active substance (or severalactive substances) is (or are) dissolved in suitable organic solvents,mixtures of solvents, water, or mixtures of organic solvents with water.As organic solvents it is possible to use polar organic solvents suchas, e.g. alkanols. The solutions should contain the active substances ina concentration of from 1 to 20%. These solutions can be applied withthe aid of sprays.

Other biocidal active substances or agents may be added to the describedagents according to the invention. For the widening of their sphere ofaction, the new agents may also contain, in addition to the statedcompounds, for example, insecticides, fungicides, bactericides,fungistratics, bacteriostatics or nematocides. The agents according tothe invention can also contain fertilisers and additionalmicronutrients, etc..

Preparations of the new active substances are described in thefollowing. The term `parts` denotes parts by weight.

Wettable powder

The following constituents are used for the preparation (a) of a 70%,(b) of a 25%, and (c) of a 10% wettable powder:

    ______________________________________                                        a)  70     parts of the monopotassium salt of the iron(III)-                             complex of Compound No. 5,                                             5      parts of sodium dibutylnaphthyl sulphonate,                            3      parts of naphthalenesulphonic acid/phenolsulphonic                            acid/formaldehyde condensate 3:2:1,                                    10     parts of kaolin,                                                       12     parts of Champagne chalk;                                          b)  25     parts of the monosodium salt of the iron(III)-                                complex of Compound No. 24,                                            5      parts of the sodium salt of oleyl methyl tauride.                      2.5    parts of naphthalenesulphonic acid/formaldehyde                               condensate,                                                            0.5    part of carboxymethylcellulose,                                        5      parts of neutral potassium aluminium silicate,                         62     parts of kaolin;                                                   c)  10     parts of the monosodium salt of the iron(III)-                                complex of Compound No. 5,                                             3      parts of a mixture of sodium salts of saturated                               fatty alcohol sulphates,                                               5      parts of naphthalenesulphonic acid/formaldehyde                               condensate,                                                            82     parts of kaolin.                                                   ______________________________________                                    

The given active substance is mixed and subsequently ground with thecarriers (kaolin and chalk). Wettable powders are obtained from whichcan be prepared, by dilution with water, stable suspensions of anydesired concentration of active substance.

Paste

The following substances are used for the preparation of a 45% paste:

    ______________________________________                                        45    parts of the monosodium salt of the iron(III)-                                complex of Compound No. 5,                                              5     parts of sodium aluminium silicate,                                     14    parts of cetyl polyglycol ether having 8 moles                                of ethylene oxide,                                                      1     part of oleyl polyglycol ether having 5 moles                                 of ethylene oxide,                                                      2     parts of spindle oil,                                                   10    parts of polyethylene glycol,                                           23    parts of water.                                                         ______________________________________                                    

The active substance is intimately mixed and ground, in suitabledevices, with the additives. A paste is obtained from which can beprepared, e.g. by dilution with the 22-fold amount of water, a 2%suspension.

We claim:
 1. A metal chelate selected from the group consisting of iron,magnesium, calcium, manganese, cobalt, nickel, copper, zinc and cadmiummetals of an asparagic acid derivative of formula I ##STR6## wherein R₁represents hydrogen, hydroxy, halogen, sulpho, carboxyl C₁ -C₆ alkyl, C₁-C₆ alkoxy, C₁ -C₆ halogenoalkyl, di- (C₁ -C₆ alkyl) amino, C₂ -C₄alkanoyl or phenyl,R₂ represents hydrogen, hydroxy, halogen, C₁ -C₆alkyl or C₁ -C₆ alkoxy, and R₃ represents hydrogen or C₁ -C₆ alkyl. 2.The metal chelates of the asparagic acid derivatives of formula Iaaccording to claim 1 ##STR7## wherein R₄ represents hydrogen, hydroxy,halogen, sulpho, carboxyl, C₁ -C₆ alkyl, C₁ -C₄ alkoxy, or phenyl, andR₅represents hydrogen, halogen, C₁ -C₆ alkyl or C₁ -C₄ alkoxy.
 3. Themetal chelate of the compound of the formula ##STR8## according toclaim
 1. 4. The metal chelate of the compound of the formula ##STR9##according to claim
 1. 5. The metal chelate of the compound of theformula ##STR10## according to claim
 1. 6. The chelate of claim 1,wherein said metal is iron (III).